This invention relates to a work material feeding device or a work material feeder for a sewing machine.
A known work material feeder for a sewing machine is equipped with a pair of pulse motors as driving sources for moving a work material holder in a longitudinal direction and another (transverse) direction perpendicular thereto within the same plane perpendicular to a vertical passageway where a needle is vertically moved. A minimum unit of the movement thereof in the longitudinal or transverse direction has been set in accordance with the minimum rotation angle of the pulse motors. For example, given the rotation angle of the pulse motors, the rotation angle divided into 200 (with a minimum divisibility of 1.8 in terms of a degree), is converted into a linear movement by using gears and belts to allow the work material holder to move by 0.1 mm or 0.2 mm of a unit.
In the conventional sewing machine, however, the divisibility of the rotation angle of the pulse motors is fixed depending on the machine model; e.g., the unit cannot be changed from 0.1 mm to 0.2 mm or vice versa. In consequence, when a fine pattern, such as embroidery, is sewn with a machine having a coarse linear movement of 0.2 mm, it is difficult to sew minute patterns, whereas when ordinary sewing, such as work material sewing or bar tacking, is carried out with a machine having a fine linear movement of 0.1 mm, the slow sewing speed decreases the efficiency of the operation of the machine. If an increase in the sewing speed is attempted in the latter case, it is necessary to improve the performance of the pulse motors and their driving circuits to a considerable extent. Accordingly, there is the problem that the machine production cost is remarkably raised.
Another problem is attributed to the fact that, since ordinary and embroidery sewing pattern data are respectively prepared with 0.2 mm and 0.1 mm as a unit, both types of data cannot be utilized simultaneously by one machine since a conventional machine typically has a fixed unit of linear movement.